1. Field of the Invention
This invention pertains generally to the field of image display systems such as, but not limited to, aircraft display systems.
2. Description of the Related Art
Synthetic Vision Systems (singularly, “SVS”) have been operating for a few years now in a wide range of aircraft; from small, General Aviation airplanes, right up to long range corporate jets; however, these systems are approved or certified for situational awareness only, with the aim of increasing flight safety by providing the flight crew with a real-time, intuitive representation of the external environment. The synthetic scene is rendered from the pilot's eye viewpoint, and typically contains the following: terrain, obstacles, rivers and lakes, and the environment of airports. While certainly enhancing the flight crew's awareness of where they are in space, and where they are relative to terrain, obstacles and the airport, the system cannot currently be used for any operational credit. That is to say there is no difference in operational capabilities between an airplane with an SVS and one without.
Similarly, Enhanced Vision Systems (singularly, “EVS”) have been operating for a few years now in a wide range of aircraft; from small, General Aviation airplanes, right up to long range corporate jets. At the time of this writing, current regulations have been established in the United States by the Federal Aviation Administration (“FAA”) addressing a specific form of EVS—an Enhanced Flight Vision System (“EFVS”)—which provides Head-Up Display (“HUD”) to provide flight information, navigation information, and a real-time image of the external scene to the pilot on one display. Unlike the SVS which provides a real-time image of the external environment by retrieving data representative of terrain, obstacles, rivers and lakes, and the environment of airports stored in databases, the EVS provides real-time images of the outside scene produced by imaging sensors which may be based upon forward-looking infrared, millimeter wave radar, low level light intensification, or other imaging technologies. In certain conditions, the EVS can enable a pilot to see the approach lighting system (“ALS”), visual references associated with the runway environment, and other objects or features that might not be visible without the use of an EVS. Combining the flight information, navigation guidance, and sensor imagery on a HUD allows the pilot to remain head up and to continue looking forward along the flight path throughout the entire approach-to-landing, landing, and after-landing.
The FAA has asserted that an EFVS might improve the level of position awareness, providing visual cues to maintain a stabilized approach and reducing the number of missed approached procedures. An EFVS could also enable a pilot to detect an obstruction on the runway, such as an aircraft or vehicle, earlier in the approach, and detect runway incursions in reduced visibility conditions. The EFVS could be used to achieve better situation awareness than might be possible without it—especially in marginal visibility conditions.
The current regulations permit the use of EFVS in lieu of natural vision to continue descent to 100 feet above the touchdown zone elevation of the runway of intended landing. At and below 100 feet, however, the lights or markings of the runway threshold or the lights or markings of the touchdown zone have to be distinctly visible and identifiable to the pilot using natural vision. A pilot cannot continue descent below 100 feet by relying solely on the EFVS sensor imagery.
At the time of this writing, the FAA has promulgated proposed regulations to permit enhanced vision provided by the EFVS to be used in lieu of natural vision to descend below 100 feet above the touchdown zone elevation. The current visual references that need to be seen using natural vision to descend below 100 feet may serve as the basis for establishing the visual references to be seen with enhanced vision to descend below 100 feet when conducting EFVS operations to touchdown and rollout. Those visual references are comprised of lights or markings of the runway threshold or lights or markings of the touchdown zone. Also, the actual runway threshold and touchdown zone surfaces could be used as references that a pilot may use to descend below 100 feet.